class Node(object):
    def __init__(self,data):
        self.data = data
        self.next = None
class Stack(object):
    def __init__(self):
        self.node = Node(None)
        self.head = self.node
        self.size = 0
    def is_empty(self):
        return self.size == 0
    def get_size(self):
        return self.size
    def push(self,data):
        node = Node(data)
        node.next = self.head.next
        self.head.next = node
        self.size += 1
    def pop(self):
        if not self.is_empty()
        current_node = self.head.next
        if self.get_size() == 1:
            self.head.next = None
            self.seze-=1
            return current_npde.data
        else:
            print("栈为空") 
    def top(self):
         if not self.is_empty():
             return self.head.next.date
         else:
             print("栈为空")
s=Stack()
s.push(1)
s.push(2)
s.push(3)
print(s.is_empty())
print(s.top())
s.pop()
s.pop()
s.pop()
